Adapt the mount to the base or the base to the mount before printing the parts.

All the holes must be reamed with a drill of the corresponding size. Check the dimensions of your axes to choose the right drill. Using a drill bit of the same size will make all the axes fitting tight, so they won't move alone.

Use a drill 0.1 mm above the axle diameter to re-drill the base where the lever is rotating, to have some play.

Check the diameter of both bearing housing, use the tail of a drill. Now you know if your printer is accurate or if you have to tune the filament's flow or slicer parameters.

Heat set the M3 insert into the base. Take care not to deviate to the filament/teflon tube side. Re-drill the teflon tube housing if needed.

Press the bearings in their housing. 

Oil the needle cages before inserting into the gears.

Insert the gear into the mount from the worm gear side. Press the axle when in place. Check if it turns freely.

Insert the gear into the lever and press the axle.

Set the lever in place and press its axle. Screw the M3 without tightening.

Grease slightly the gears and insert the worm gear into the base.

Mount the Flextruder over the head. The teflon tube must protrude from the heat sink 4-5 mm to center the extruder over it.

Insert the flexshaft into the cap. Line up the shaft with the worm screw. Tighten the 3 M2.5 screw reasonably... It doesn't need to move, that's all.

The flexshaft sheath must have a little play, so push it down on the cap until it blocks and pull it about 1 mm before tightening the screw.

Check on the other side of the flexshaft if it rotates freely.

If it doesn't check why before mounting any motor on the shaft.

Mount the motor.

Set the motor's current to be as low as possible: The lowest current will also give you the highest speed and acceleration. Too much current means too much torque, and the weak link is the plastic worm screw... I drive a 4 ohm NEMA 17-23 motor with 0.3 A @ 12 V... It can push as much filament as the heater can make flow and will stall before the worm gear break.

The lever pressure is adjusted with the filament in place. Look at the dents on the filament to determine the right pressure. The filament should not slip before the motor stalls... Try to stop pulling the filament with your fingers, It will give you an idea of the force level that this system can develop.

The reference parameter for the filament flow is 1.3 mm/ motor turn or 150 full steps/mm. Adapt your firmware and make some extrusions tests to fine-tune.

It can be done simply by removing the heat block and compare the filament effectively extruded with what you wanted to have, and correct the parameter accordingly.

Check the maximum speed that you can reach before the motor stalls. Use a low acceleration at first. Then stay about 10% below stall speed and increase the acceleration until it stalls again.

Now you're ready to tune the printer's retraction and pressure advance.